[Bug 1704106] Re: [SRU] Gathering of thin provisioning stats breaks c-vol

[OpenStack Infra]

Reviewed:  https://review.openstack.org/644232
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=b1a0d62f357e431a6b74d38440a8392de972b824
Submitter: Zuul
Branch:    stable/ocata

commit b1a0d62f357e431a6b74d38440a8392de972b824
Author: Gorka Eguileor <geguileo at redhat.com>
Date:   Tue Feb 6 14:54:57 2018 +0100

    RBD: Don't query Ceph on stats for exclusive pools
    
    Collecting stats for provisioned_capacity_gb takes a long time since we
    have to query each individual image for the provisioned size.  If we are
    using the pool just for Cinder and/or are willing to accept a potential
    deviation in Cinder stats we could just not retrieve this information
    and calculate this based on the DB information for the volumes.
    
    This patch adds configuration option `rbd_exclusive_cinder_pool` that
    allows us to disable the size collection and thus improve the stats
    reporting speed.
    
    Change-Id: I32c7746fa9149bce6cdec96ee9aa87b303de4271
    Closes-Bug: #1704106
    (cherry picked from commit f33baccc3544cbda6cd5908328a56096046657ed)
    (cherry picked from commit 21821c16580377c4e6443d0b440f41cb7de0ca8d)
    (cherry picked from commit 1dca272d8f47bc180cc481e6c6a835eda0bb06a8)


** Changed in: cloud-archive/ocata
       Status: New => Fix Committed

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https://bugs.launchpad.net/bugs/1704106

Title:
  [SRU] Gathering of thin provisioning stats breaks c-vol

Status in Cinder:
  Fix Released
Status in Ubuntu Cloud Archive:
  New
Status in Ubuntu Cloud Archive ocata series:
  Fix Committed
Status in Ubuntu Cloud Archive pike series:
  Fix Released

Bug description:
  [Impact]

  Backport config option added in Queens to allow disabling the
  collection of stats from all rbd volumes since this causes
  tons of non-fatal race conditions and slows down deletes to
  the point where the rpc thread pool fills up blocking further
  requests. Our charms do not configure pool by default and we
  are not aware of anyone doing this in the field so this patch
  enables this option by default.

  [Test Case]

  By default no change in behaviour should occur. To test the
  new feature we need to enable it i.e.:

  * deploy openstack ocata
  * set rbd_exclusive_cinder_pool = true in cinder.conf
  * create 100 volumes via cinder
  * also create 100 volumes from the cinder pool but using the rbd client directly
  * delete cinder volumes (via cinder) and delete the non-cinder rbd volumes using rbd client
  * ensure there are no exceptions in cinder-volume.log

  [Regression Potential]
  The default behaviour is unchanged so no regression is expected.

  ==========================================================================

  The gathering of the thin provisioning stats is done by looping over
  all volumes:

  https://github.com/openstack/cinder/blob/master/cinder/volume/drivers/rbd.py#L369

  For larger deployments, this loop (done at start-up, upon volume
  deletion and as periodic a task) is taking too long and hence breaks
  the c-vol service.

  From what I understand, the overall idea of this stats gathering is to
  bring the current real fill status of the pool to the admin's
  attention in case over-subscription was configured. For this, a fill
  status at the pool level (rather than the volume level) should be good
  enough.

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